package jjn.acwing.java_basic;

import java.util.Scanner;

/**
 * @author Jjn
 * @since 2023/9/5 22:56
 */
public class Acwing772 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            String s = scanner.next();
            int[] index = new int[26];
            for (int i = 0; i < s.length(); i++) {
                index[s.charAt(i) - 'a']++;
            }
            int i = 0;
            for (; i < s.length(); i++) {
                if (index[s.charAt(i) - 'a'] == 1) {
                    System.out.println(s.charAt(i));
                    break;
                }
            }
            if (i == s.length()) {
                System.out.println("no");
            }
        }
    }
}
